Synthesis of pyrrolo[2,3-d]pyridazines and pyrrolo[2,3-c]pyridines (6-azaindoles). Experimental and theoretical study

A new synthetic route towards 6-azaindoles (pyrrolo[2,3-c]pyridines) and pyrrolo[2,3-d]pyridazines starting from 4-aroyl pyrroles is described. This overall protocol involves: (i) the Vilsmeier–Haack reaction to obtain pyrrolo-2,3-dicarbonyles and (ii) condensation with hydrazines or glycine methyl ester. The reaction mechanism between pyrrolo-2,3-dicarbonyl with phenyl hydrazine and glycine methyl ester has been modelled using DFT calculations to prove the formation of one from two possible isomers of condensation.